Radioactive Decay. What do you know about Radioactivity? 1.All atoms are made up of __________....
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Transcript of Radioactive Decay. What do you know about Radioactivity? 1.All atoms are made up of __________....
![Page 1: Radioactive Decay. What do you know about Radioactivity? 1.All atoms are made up of __________. 2.What are some radioactive isotopes? 3.Why do some isotopes/atoms.](https://reader035.fdocuments.us/reader035/viewer/2022062216/56649da25503460f94a8e360/html5/thumbnails/1.jpg)
Radioactive Decay
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What do you know about Radioactivity?
1. All atoms are made up of __________.
2. What are some radioactive isotopes?
3. Why do some isotopes/atoms break down and decay?
4. What is given off as atoms break down and decay?
5. How can we manipulate and use this process to our advantage?
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The Nucleus
• Recall that atoms are composed of protons, neutrons, and electrons.
• The nucleus of an atom contains the protons, which have a positive charge, and neutrons, which have no electric charge.
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The Strong Force
• How do you suppose protons and neutrons are held together so lightly in the nucleus?
• Another force, called the strong force, causes protons and neutrons to be attracted to each other.
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• Protons and neutrons have to be close together, like they are in the nucleus, to be attracted by the strong force.
The Strong Force
• The strong force is a short-range force that quickly becomes extremely weak as protons and neutrons get farther apart.
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Attractions and Repulsion
• Some atoms, such as uranium, have many protons and neutrons in their nuclei.
• These nuclei are held together less tightly than nuclei containing only a few protons and neutrons.
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• If a nucleus has only a few protons and neutrons, they are all close enough together to be attracted to each other by the strong force.
Attractions and Repulsion
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• If nuclei have many protons and neutrons, each proton or neutron is attracted to only a few neighbors by the strong force.
Forces in a Large Nucleus
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Radioactivity• When the strong force is not large enough
to hold a nucleus together tightly, the nucleus can decay and give off matter and energy. Larger elements are more unstable and tend to decay.
• This process of nuclear decay is called radioactivity.
• All nuclei that contain more than 83 protons are radioactive.
• However, many other nuclei that contain fewer than 83 protons also are radioactive.
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Radioactivity
• Almost all elements with more than 92 protons don’t exist naturally on Earth.
• They have been produced only in laboratories and are called synthetic elements.
• These synthetic elements are unstable, and decay soon after they are created.
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Isotopes
• Nuclei that have the same number of protons but different numbers of neutrons are called isotopes.
• These two isotopes of helium each have the same number of protons, but different numbers of neutrons.
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• Nuclei with too many or too few neutrons compared to the number of protons are radioactive and decay too.
Stable and Unstable Nuclei
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Nuclear Radiation
• The three types of nuclear radiation are alpha, beta (BAY tuh), and gamma radiation.
• Alpha and beta radiation are particles. Gamma radiation is an electromagnetic wave.
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Nuclear Radiation
• When an unstable nucleus decays, particles and energy called nuclear radiation are
emitted from it.
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Alpha Particles
• When alpha radiation occurs, an alpha particlemade of two protons and two neutrons is emitted from the decaying nucleus.
• Notice that the alpha particle and its symbol is the same as a helium nucleus,
• In alpha decay, two protons and two neutrons are lost from the nucleus or Helium gas is released.
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Beta Decay
• Sometimes in an unstable nucleus a neutron decays into a proton and emits an electron.
• The electron is emitted from the nucleus and is called a beta particle.
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Gamma Rays
• They have no mass and no charge and travel at the speed of light.
• The properties of gamma rays are summarized in the table.
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• Thick blocks of dense materials, such as lead and concrete, are required to stop gamma rays.
Gamma Rays
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Alpha Decay
Beta Decay
Gamma Radiation
What is released?
Radiation is made of… (Particles or electromagnetic waves)
Interesting Fact (Use pgs 541-543)
Standard: SPS3a Students will differentiate between alpha, beta decay and gamma radiation
What is Nuclear Radiation?
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Reading Assignment
• Please read pgs 544-545 on Radioactive Half-life.
• As you read please make notes over the following sections:
Section Your Notes
Radioactive half-life
Radioactive Dating
Carbon Dating
Uranium Dating
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Radioactive Half-Life
• Some radioisotopes decay to stable atoms in less than a second.
• However, the nuclei of certain radioactive isotopes require millions of years to decay.
• A measure of the time required by the nuclei of an isotope to decay is called the half-life.
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Radioactive Half-Life
• The half-life of a radioactive isotope is the amount of time it takes for half the nuclei in a sample of the isotope to decay.
• The nucleus left after the isotope decays is called the daughter nucleus.
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• Half-lives vary widely among the radioactive isotopes.
Radioactive Half-Life
• Some geologists, biologists, and archaeologists, among others, are interested in the ages of rocks and fossils found on Earth.
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• The number of half-lives is the amount of time that has passed since the isotope began to decay.
Radioactive Dating
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• Carbon-14 has a half-life of 5,730 years and is found in molecules such as carbon dioxide.
Carbon Dating
• Plants use carbon dioxide when they make food, so all plants contain carbon-14.
• Only material from plants and animals that lived with the past 50,000 years contains enough carbon-14 to be measured.
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Common Isotopes
• Polonium-214 has a half life of .7 sec
• Uranium-238 = 4.5 billion years
• Carbon-14 = 5,730 years
• Lead-212 = 10.6 hours
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Problems
• If a human body contained 50 grams of C-14 and now had only 25 g, how old is the body?
• ½ of 50 is 25 so 1 half-life elapsed and that is 5,730 years
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Problems
• If the amount of C-14 is 12.5 g
• 11,460 years
• If the amount of C-14 is 6.25g
• 17,190 years
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Graphs of Radioactive Decay
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Detecting Radiation